1. Field of the Invention
The present invention relates to multiple-layer polymeric tubing, and more particularly, to a filler neck made from such tubing.
2. Discussion
Filler necks provide a flow path between a motor vehicle's fuel tank and an external fuel source. Originally, filler necks were constructed from metal tubes that were attached to the fuel tank by brazing. Later, brazing was replaced by the use of mechanical connectors. More recently, manufacturers have introduced filler necks made from tubes comprised of one or more polymeric layers. Although conventional polymeric filler necks exhibit certain advantages over metallic filler necks--including weight reduction, improved stability during collisions, and cost savings--they are not without problems.
For example, a filler neck must often be bent at points along its length to conform to unique space requirements in a particular motor vehicle. Bending the filler neck may, depending on the severity of the bend angle, the rigidity of the polymer, and the hoop strength of the tube, produce kinks that obstruct fuel flow. Although kinks can often be avoided by heating the filler neck and supporting it along the bend radius during a bending operation, such procedures are time consuming and require additional equipment such as bending fixtures and ovens.
Although polymeric materials used in current filler neck designs perform satisfactorily, improvements are needed. Most non-metallic filler necks are made from polyamides, including Nylon 6, Nylon 6.6, Nylon 11 and Nylon 12. There are many reasons for their widespread use: polyamides resist attack by fuels and fuel additives, are easily and quickly processed, are recyclable, and are available in standard, uniform grades. However, polyamides, and filler neck tubes made entirely from one or more polyamide layers, provide less flame retardancy and abrasion resistance than other melt processible polymers.
Furthermore, filler neck tubing made entirely of polyamides may not meet stringent air pollution standards. It is anticipated that future Federal and state regulations will limit permissible hydrocarbon emissions due to permeation through fuel lines, vapor recovery hoses, and filler neck tubing. For example, regulations that will be enacted in California fix the total passive hydrocarbon emission for a motor vehicle at 2 g/m.sup.2 per 24 hour period as calculated by evaporative emission testing methods such as those described in Title 13 of the California Code of Regulations, section 1976, proposed amendment of Sep. 26, 1991. To achieve the desired total vehicle emission levels, a hydrocarbon permeation level equal to or below 0.5 g/m.sup.2 per 24 hour period would be required.
Finally, filler necks made of polymeric materials are susceptible to degradation by electrostatic discharge. Because polymeric materials are generally poor electrical conductors, fuel flowing through the polymeric filler tube imparts an electric charge to the filler neck. The electric charge accumulates on the filler tube until it is large enough to discharge into a nearby electrical conductor. This charge is repeatedly replenished with the passage of additional fuel through the tube. The electrostatic discharge repeatedly occurs in a localized area, gradually eroding the area and leading to rupture of the tubing.
The present invention is directed to overcoming, or at least minimizing, one or more of the problems recited above.